Ventilation method and apparatus with dust collection by electric static precipitator

ABSTRACT

A method for electrostatic dust collection which comprises introducing a dust particle- or mist-containing high temperature gas formed in the lower portion of a building into a dustcollecting passage provided with a charging electrode and a dustcollecting electrode face, said dust-collecting passage being formed in a ventilating chamber provided in the upper portion of the building and connected with both a suction port mounted at the lower end of said ventilating chamber and an exhaust port mounted on a roof or side wall of said ventilating chamber; forwarding said dust particle or mist-containing high temperature gas through said dust-collecting passage in which an electrostatic field is formed, along said charging electrode and substantially in parallel thereto; thus catching dust particles or mists contained in the gas on the dust-collecting electrode face; and discharging the gas into the exterior of the ventilating chamber, and apparatus therefor.

United States Patent 11 1 Y 1111 3,844,205

Watanabe Oct. 29, 1974 [54] VENTILATION METHOD AND APPARATUS 3,260,1897/1966 Jensen 98/115 K WITH DUST COLLECTION BY ELECTRIC 2,223,332 {32;":(a lan 12 7 52/35;

6 mar STATIC PRECIPITATOR 3,618,659 11 1971 Rawal 165/107 x [75]inventor: Tamotsu Watanabe, Tokyo, Japan 3,729,399 4/1973 Kibby 204/67.[73] Assignee: Nippon Kogei Kogyo Co., Ltd.,

3,747,301 7/1973 Glover et al. 55/467 X Tokyo Japan PrimaryExaminer-Dennis E. Talbert, Jr. [22] Filed: Oct. 25, 1972 Attorney,Agent, or Firm-Sherman & Shalloway 21 Appl. No.2 300,707

[57] ABSTRACT [30] Foreign Application Priority Data A method forelectrostatic dust collection which com- Nov. 5, 1971 Japan 46-87581prises introducing a dust particleof misvcomaining Nov. 6, 1971 Japan46-87981 high temperature gas formed in the lower Portion of a buildinginto a dust-collecting passage provided with a [52] I LS. Cl 98/115 R,55/13, 55/119, charging electrode and a dust collecfing electrode ZQL l1/li93 5l 5. 1 28 face, said dust-collecting passage being formed in a55/240 55,385 SSIDIG' 75/25 ventilating chamber provided in the upperportion of 1 98/36 266/15 mthe building and connected with both asuction port [51] I Cl Bosc 3/28 B03: 3/41 B036 3/53 mounted at thelower end of said ventilating chamber Fleld of Search 55/ 124, 126, 146,151, and an exhaust port mounted on a roof or Side wall of 55/149, 2said ventilating chamber; forwarding said dust particle 385; 98/36 115115 K; 75/25; 266/15 or mist-containing high temperature gas throughsaid 17, 19 dust-collecting passage in which an electrostatic field isformed, along said charging electrode and substan- [56] 1 ReferencesCited tially in parallel thereto; thus catching dust particles or UNITEDSTATES PATENTS mists contained in the gas on the dust-collecting elec-1,339,480 5/1920 Schmidt 55/119 X trode face; and discharging the gasinto the exterior of 2,756,842 1 m r in et /l2 X the ventilatingchamber, and apparatus therefor. 3,064,409 11/1962 Schmidt 55/122 a3,238,702 3/1966 DeSeversky 55/119 13 Chums, 10 Drawlllg Figures 1VENTILATION METHOD AND APPARATUS WITH DUST COLLECTION BY ELECTRIC STATICPRECIPITATOR This invention relates to a method and apparatus forcollecting dust electrostatically. More particularly, the inventionrelates to a method for electrostatic dust collection in which a dustparticle-or mist-containing gas formed inside a building is directlyintroduced into a ventilating chamber provided in the upper portion ofthe building and the electrostatic dust collection is effected in saidventilating chamber, and to an apparatus for practising this method.

Heretofore, in blast furnaces of iron mills, an operation of taking outmolten pig iron in a blast furnace from a tap hole provided on aso-called casting house and introducing it through an iron runnerprovided on the floor of the casting house to mixing car is repeatedseveral times per day. At this iron delivery operation, fumes of fineiron oxide rise from molten pig iron and these fumes of iron oxide aredischarged as smoke in the air from a ventilating chamber (monitor).Accordingly, in a building of the casting house, a crane, an iron knochopener, a mud gun, etc. are provided for opening (boring) or closing tapholes. Further, repair and maintenance of the iron runner and inspectionof molten pig iron should be effected. Therefore, it is generallydifficult to provide equipment for dust collection or smoke discharge inthe building of the casting house,

. and hence, in the actual working a gas containing particles of ironoxide, which is formed at the operation of molten iron delivery, isdischarged directly in the air.

It may be considered to collect dust from such high temperature gascontaining particles of dust by providing a smoke exhaust duct andintroducing the dust particlecontaining gas through this duct to acustomary Cottrell precipitator. The customary Cottrell precipitatoraccomplishes dust collection electrically by passing a dustparticle-containing gas through an electric field formed betweenconfonting electrodes. However, the dust catching efficiency by theCottrell precipitator is low, especially in the case of fine particles.For instance, dust particles having a size less than 1 micron cannot beeffectively caught by the Cottrell precipitator. Furthermore, when it isintended to conduct both smoke discharge and dust collection effectivelywhile preventing the building of the casting house from being filledwith fumes of iron oxide formed at the molten iron delivery operation,it is necessary to provide extremely large duct, fan and dust collector.However, provision of such equipment is quite impossible from the actualstandpoint.

Not only in a building of the above mentioned casting house of a blastfurnace, but also in buildings of an open-hearth furnace and a converterin an iron mill, a building of a casting house in an iron foundry andbuildings of chemical factories provided with a calcination furnace, aroasting furnace, a drying furnace, a melting furnace and the like, dustparticleor mistcontaining high temperature gases are similarly formed inworking areas of such buildings, and performance of dust collection isrequired.

It is a primary object of this invention to provide a method andapparatus in which a dust particle-or mistcontaining high temperaturegas formed in a working area of a building can be directly subjected tothe electrostatic dust collection operation in a ventilating chamberprovided in the upper portion of the building,

Another object of this invention is to provide a method and apparatus inwhich a dust particleor mistcontaining high temperature gas formed in aworking area of a building can be introduced directly to a ventilatingchamber provided in the upper portion of the building by utilizing theupward current of this gas and the electrostatic dust collection can beeffectively ac complished in this ventilating chamber.

Still another object of this invention is to provide a method andapparatus for electrostatic dust collection in which a dust particleormist-containing high temperature gas fonned in a working area of abuilding can be subjected to the dust collection operation in aventilating chamber provided in the upper portion of the buildingwithout employing an exhaust duct or exhaust fan and without reductionof the operation efficiency in the working area of the building.

A further object of this invention is to provide a method and apparatusfor dust collection in which an iron oxide fume formed in a castinghouse is moved toward the upper portion of the casting house building inthe form of an upward curent in a space surrounded by an upward currentof a gas different from the iron oxide fume-containing gas whilepreventing the working area of the casting house building from beingfilled with the iron oxide fume, to thereby introduce the iron oxidefume into a dust collector mounted in a ventilating chamber provided inthe upper portion of the casting house building, and thus particles ofiron oxide can be effectively removed.

A still further object of this invention is to provide a method andapparatus for removing an iron oxide fume formed in a casting house, inwhich examination or inspection of molten pig iron delivered can beconducted with ease and a danger of workers falling into an irondelivery passage can be greatly reduced.

In accordance with this invention, there is provided a method forelectrostatic dust collection which comprises introducing a dustparticleor mist-containing high temperature gas formed in the lowerportion of a building into a dust-collecting passage provided with acharging electrode of a fine wire form and a dustcollecting electrodeface confronting to the charging electrode, said dust-collecting passagebeing formed in a ventilating chamber provided in the upper portion ofthe building and connected with both a suction port mounted at the lowerend of said ventilating chamber and an exhaust port mounted on a roof orside wall of said ventilating chamber; forwarding said dust particleormist-containing high temperature gas through said dust-collectingpassage in which an electrostatic field is formed between said chargingelectrode of a fine wire form and said dust-collecting electrode face,along said charging electrode of a fine wire form and substantially inparallel thereto; thus catching dust particles or mists contained in thehigh temperature gas on the dust collecting electrode face; anddischarging the gas from which dust particles or mists have beensubstantially removed, into the exterior of the ventilating chamber.

In accordance with this invention, there is also provided an apparatusfor electrostatic dust collection which comprises a working areaprovided in the lower portion of a building in which a dust particle-ormistcontaining high temperature gas is formed; a ventilating chamberprovided in the upper portion of the building, said ventilating chamberbeing connected with said working area through a suction port mounted atthe lower end of the ventilating chamber and opened to the open airthrough an exhaust port mounted on a roof or side wall of theventilating chamber; and a dustcollecting passage formed in saidventilating chamber and composed of a charging electrode of a fine wireform supported by an insulating member and a dustcollecting electrodeface confronting to said charging electrode, an electrostatic fieldbeing formed between said charging electrode and said dust-collectingelectrode face; said dust-collecting passage having such a length thatthe residence time of the dust particleor mist-containing gas passingthrough the inside of the dust-collecting passage by natural convectionis at least seconds, and said charging electrode of a fine wire formbeing laid along the direction of the advance of the dust particleormist-containing gas in the dustcollecting passage.

The invention will now be described by reference to embodimentsillustrated in accompanying drawings in which:

FIG. 1 is a partially cut-out side view showing a casting house in ablast furnace;

FIG. 2 is a ground plan illustrating the plan arrangement of the castinghouse shown in FIG. 1;

FIG. 3 is a view explaining formation of an iron oxide fume;

FIG. 4 is a sectional view illustrating the front of a ventilatingchamber according to one embodiment of this invention;

FIG. 5 is a partially broken perspective view showing the ventilationchamber illustrated in FIG. 4;

FIG. 6 is a view illustrating the section of a dustcollecting psspassage according to another embodiment of this invention and alsoshowing diagramatically the dust-collecting system;

FIG. 7 is a sectional view illustrating a dust-collecting passageaccording to still another embodiment of this invention;

FIG. 8 is an arrangement plan illustrating the state of fitting of acharging electrode of a fine wire form shown in FIG. 7;

FIG. 9 is a sectional view illustrating the side of one embodiment ofdust-collecting apparatus of this invention; and

FIG. 10 is a cross-sectional view taken along the line X-X in theapparatus shown in FIG. 9.

In FIG. 1, a furnace proper 2 of a blast furnace is supported verticallyby a blast furnace stanchion l, and a tap hole 4 is provided on a hearth3 of the furnace proper 2 or in the vicinity of the hearth. One or aplurality of such tap holes 4 are formed around the furnace proper 2. Acasting house 5 is provided circumferentially or radially to surroundthe hearth 3 of the furnace proper 2, and is supported by a stanchion 6.On the floor of the casting house 5, there is provided an iron runner 7(iron passage) for take-out of molten pig iron, which extends from thetap hole 4 straightly or radially in the appropriately branched form.Molten pig iron flowing out of the tap hole 4 moves on said runner andis charged into a mixing car 8 standing by below the casting house. Abuilding 10 is provided above the floor of the casting house 5 andsupported by a stanchion 9. The inside of the building 10 forms aworking area. An iron knoch opener (not shown) for opening the tap holeat the time of molten iron delivery or a mud gun (not shown) for closingthe tap hole at the end of the molten iron delivery operation is adaptedinside the building 10 at a part adjacent to a furnace body 12. Aring-like blast main 13 is disposed around the furnace body 12 to feedhot air into the furnace. In the interior of the building 10, a crane 11is mounted to transfer materials and devices necessary for operations atthe casting house. In the upper portion of the building 10, aventilating chamber 14, i.e., a small chamber generally called amonitor, is provided to discharge an iron oxide fume formed at thecasting house 5 to the exterior of the building 10. The lower side ofthis ventilating chamber 14 is opened to the interior of the buildingIt) and an exhaust chamber 14 is openedto the interior of the building10 and an exhaust port is mounted on a roof or side wall of theventilating chamber 14.

At the time of molten iron delivery, a seal of the tap hole is opened bythe iron knoch opener and molten pig iron stored at the hearth 3 of theblast furnace is allowed to flow on the iron runner 7 of the castinghouse 5 from the tap hole 4 and charged into the mixing car 8 through abranched runner 7-a or 7-b and a shoot 7-c, as shown in FIG. 2. Slugcoming out together with molten pig iron is withdrawn to a slug tank 16through a passage 7 mounted on a tap hole 4'. At this time, a greatquantity of an iron oxide fume rises from the vicinity of the tap hole 4(hereinafter referred to as the tap hole portion) and from the runner 7of the casting house 5, as shown in FIG. 3, and this iron oxide fumefills the working area of the building 10 and a part of the fume isdischarged as a smoke into the air from the ventilating chamber providedin the upper portion of the building 10. Accordingly, the atmosphere ofthe working area ofthe casting house is extremely contaminated with thisiron oxide fume, resulting in degradation of the working environment andcausing serious problems on health maintenance of workers. Further, itis generally said that the amount of iron oxide dust discharged in theair by the molten iron delivery operation is in an order of a ton perday, and this causes a serious pollutional problem.

The most important feature of this invention is that a dust-collectingpassage composed of a charging electrode of a fine wire form supportedby an insulating member and a dust-collecting electrode face confrontingthereto is provided in the above-mentioned ventilating chamber so thatan electrostatic field is formed between said charging electrode anddust-collecting electrode face and a dust particleor mist-containinghigh temperature gas formed in the working area positioned in the lowerportion of the building is introduced in the form of an upward currentinto said dustcollecting passage and forwarded in the dust-collectingpassage along said charging electrode substantially in parallel thereto,whereby dust particles or mists contained in the gas can beelectrostatically collected effectively.

More specifically, it has been found that the dust particleormist-containing high temperature gas to be flown into the ventilatingchamber (monitor) in the form of an upward current has a linear velocitywithin a range most preferred for effecting the electrostatic dustcollection, and that when this dust particleor mist-containing gas isnaturally passed through the dust-collecting passage composed of acharging electrode of a fine wire form and a dust-collecting electrodeface confronting thereto, along said charging electrode of a fine wireform and substantially in parallel thereto, the dust collection can beaccomplished very effectively with a relatively short length of thedust-collecting passage, as compared with any of conventional dustcollectors employing a suction fan or an exhaust fan. Based on thisfinding, the invention has been achieved. Further, in this invention,since the whole mechanism for the dust collection is containedcompletely inside the ventilating chamber projecting in the upperportion of the building, the working efficiency in the interior of thebuilding is not degraded at all.

For attaining the above feature, the ventilating chamber (monitor)indicated as a whole by reference 14 in FIGS. 4 and 5 is provided. Theventilating chamber 14 has side walls 16 and 16 extending vertically toroofs l5 and 15' of the building, and the upper ends of side walls 16and 16' are connected with roof members 17 and 17', respectively. Theroof members 17 and 17' have an opening 18 at the head thereof, and acap 18 is mounted to cover this opening completely. The inside of theventilating chamber is connected with the open air through exhaust ports19 and 19 formed between the side edges of the cap 18 and the roofmembers l7 and 17. A suction port 20 is provided at the lower end of theventilating chamber 14, and the ventilating chamber 14 is connected withthe inside of the building through this suction port 20. The structureof the ventilating chamber is not limited to one illustrated in FIGS. 4and 5, but exhaust ports may be formed at the upper ends of side walls16 and 16' of the ventilating chamber 14, or gutters may be providedbelow the openings of roof members 17 and 17'. In the ventilatingchamber 14 shown in FIGS. 4 and 5, the entire of the lower end thereofis opened to form a suction port 20, but only a part of the lower endmay be opened to form a suction port, or a wire net or foraminated platemay be provided at the lower end of the ventilating chamber 14 as amember acting as a suction port.

In accordance with this invention, a dust-collecting passage composed ofa charging electrode 21 (21') of a fine wire form and a confrontingdust-collecting electrode 22 is provided to extend from the suction port20 to the exhaust port 21. It is important that the dustcollectingpassage has such a length that the residence time of a dust particleormist-containing gas passing through the inside of the passage in theform of an upward current owing to natural convection is at least 5seconds, preferably at least seconds, and that the charging electrode 21of a fine wire form is provided along the direction of the advance ofthe dust particleor mist-containing gas in the dust-collecting passage.In case the length of the dust-collecting passage is so short that theresidence time is shorter than 3 seconds, removal of dust particles ormists, especially those having a size less than I t, cannot beaccomplished effectively. From this point, the length of thedust-collecting passage is so adjusted that the residence time of thegas in the dust-collecting passage is at least 5 seconds, preferably atleast 10 seconds. On the other hand, in case the length of thedust-collecting passage is so long that the residence time is more thanseconds, any particularly prominent effect cannot be obtained but theloss of the pressure of the dust particleor mist-containing gas becomesgreat and the equipment cost becomes high. Accordingly, it is preferredthat the length of the dust-collecting passage is so adjusted that theresidence time of the gas in the dust-collecting passage is 10 to 15seconds. Further, in this invention, by providing the electrode 21 (21)of a fine wire form along the direction of the advance of the dustparticleor mistcontaining gas passing through the inside of thedustcollecting passage, it is made possible to move floatingly dustparticles or mists in the direction traversing the electrostatic fieldformed between the charging electrode of a fine wire form and theconfronting dustcollecting electrode, and therefore, even when theresidence time is relatively short, the dust collection can beaccomplished effectively. In this invention it is most preferred that,as is illustrated in FIGS. 4 and 5, the dust-collecting passage isformed vertically and the charging electrode of a fine wire form is alsolaid vertically, but as far as the loss of the pressure of the dustparticle or mist-containing gas is not extremely great, thedust-collecting passage and the electrode of a fine wire form may beprovided in an oblique to lateral direction.

In this invention, the dust-collecting passage and the chargingelectrode of a fine wire form to be laid in said passage are arranged inthe above-mentioned manner and at the same time, the dust particleormistcontaining gas is allowed to pass through the dustcollecting passagein the form of an upward current, whereby fine dust particles or mistscan be caught without use of an exhaust duct or fan at such a highcatching efficiency as cannot be expected in conventional electrostaticdust collectors. In the case of natural ventilation, the linear velocityof the dust particleor mistcontaining gas running through the inside ofthe dustcollecting passage is generally within a range of from 0.3 to 3m/sec. Accordingly, it is prefered that arrangements are made so thatthe linear velocity of the dust particleor mist-containing gas runningthrough the inside of the dust-collecting passage is within a range offrom 0.3 to 3 m/sec, especially from 0.5 to 2 m/sec. At a linearvelocity lower than 0.3 m/sec, a sufficient removal of smoke from thebuilding cannot be attained and the building is sometimes filled withsmoke. In order to attain a linear velocity higher than 3 m/sec, it isnecessary to make the length of the dust-collecting passage too great.Therefore, either too high a linear velocity or too low a linearvelocity is not preferred.

It is preferred that the diameter of the charging electrode 21 (21) of afine wire form is, for instance, less than 1 mm, especially 0.3 to 0.6mm. This charging electrode of a fine wire form provides an effectiveelectric field of corona discharge between the charging electrode andthe confronting dust-collecting electrode, and the activity of chargingfloating dust particles or mists is much higher than the chargingactivity of the electrode in the conventional Cottrell precipitator.Thus, electrification and collection of fine dust particles or mists canbe accomplished very effectively. A voltage applied between the chargingelectrode and dust-collecting electrode varies depending on the kind ofthe dust to be removed, the distance between both the electrodes andother factors, but in general, it is preferred that a voltage of to 200KV, especially to KV, is applied between both the electrodes. In thecase of a voltage lower than 100 KV, sufficient dust-collecting effectscannot be attained, and in the case of a high voltage exceeding 200 KV,any particular advantage cannot be attained by increasing the voltagebut practical difficulties are brought about in connection with highvoltage-generating apparatus or insulating members. In general, thedistance between the charging electrode and dust-collecting electrode is40 to 100 cm, preferably 50 to 80 cm. In case this distance is greaterthan 100 cm, sufficient dust-collecting effects cannot be obtained, andon the other hand, when this distance is smaller than 40 cm, thecross-sectional area of the dust-collecting passage through which thegas is allowed to run becomes small, resulting in economicaldisadvantages. In this invention it is especially desired that thedistance between both the electrodes and the voltage are so chosen thatan average fieldintensity in the dust-collecting passage is from 1.0 to2.5 KV/cm. The length of the dust-collecting passage varies depending onthe kind of the dust or mist to be removed, but in general, the lengthis selected within a range of from 2 to 20 m, especially from 4 to m, soas to maintain the residence time and linear velocity of the gas at theabove-mentioned levels.

Various installing methods may be adopted for providing the chargingelectrode 21 of a fine wire form and the dust-collecting electrode 22 inthe ventilating chamber 14. For instance, as is illustrated in FIGS. 4and 5, insulating members 23 (23') such as porcelain insulators aremounted on the upper and lower ends of the side wall 16 (16') of theventilating chamber 14, and the charging electrode 21 (21 of a fine wireform is kept tight on the end points of insulating members 23 (23').Dust-collecting electrode plates 22 are fitted in the ventilatingchamber 14 in parallel to such charging electrodes 21 (21) of a finewire form, and a certain distance such as mentioned above is formedbetween the corresponding charging electrode 21 and dustcollectingelectrode plate 22. A plurality of pairs of such charging electrodes 21(21') of a fine wire form and dust-collecting electrode plates 22 may beprovided in the ventilation chamber 14 to form a plurality ofdust-collecting passages in the ventilating chamber. In other words, aplurality of dust-collecting electrode plates are provided so as to actas partition plates for a plurality of dust-collecting passages. As isillustrated in FIGS. 4 and 5, dust-collecting electrode plates 22 may beprovided either in the widthwise direction of the ventilating chamber orin the lengthwise direction of the ventilating chamber.

In this invention, the charging electrode 21 (21) of a fine wire form isconnected with the negative terminal on the output side of a highvoltage generator 25 (25') through a high voltage cable 24 (24'), andthe dustcollecting electrode plate 22 is connected with the positiveterminal on the output side of the high voltage generator 25 (25'). Suchstructure of the electrodes is preferred because in such construction ofthe electrodes electrical charging of dust particles or mists runningthrough between both the electrodes can be accomplished stably andeffectively.

In the structure of the dust-collecting passage illustrated in FIGS. 4and 5, insulators 23 (23) are exposed to the dust-collecting passage,and therefore, dust particles or mists tend to deposit on the exposedsurfaces of the insulators, sometimes resulting in breakage ofinsulation in the insulator. In order to prevent occurrence of thisundesired insulation breakage, it is preferred to provide spout ornozzle 26 (26') on the side walls 16 (16') on which insulators 23 (23')are mounted, at parts close to such insulators 23 (23'), and to disposetube-like guides 27 (27) so as to wrap the spout or nozzle 26 (26') andthe insulators 23 (23'), so that gas stream coming from the spout ornozzle 26 (26') wipe away dust particles or mists being depositing onthe insulators. For this purpose, a suitable gas is introduced from acontamination-preventive gas supply source 28 (28) to the spout ornozzle 26 (26) through a duct 29 (29) and a distribution duct 30 (30),and is flown around the insulator from the spout or nozzle 26 (26).

In practising the method of this invention, an iron oxide fume formedfrom a tap hole 4 and an iron runner 7 of a casting house 5 shown inFIG. 1 moves upwardly in a building 10 in the form of an upward currentowing to natural convection, and reaches a suction port 20 of aventilating chamber 14 provided in the upper portion of the building 10.The iron oxide dust particle-containing gas which reaches the suctionport 20 rises gradually by natural ventilation in a dustcollectingpassage composed of a charging electrode 21 (21') of a fine wire formand an electrode plate 22, between which an electrostatic field isformed, whereby dust particles of iron oxide are arrested on the surfaceof the dust-collecting electrode 22 effectively while they aretravelling through such dust-collecting passage of a relatively shortlength. The gas from which dust particles of iron oxide have beensubstantially removed is discharged into the open air through an exhaustport 19 (19) of the ventilating chamber.

Dust particles depositing on the surface of the dustcollecting electrode22 of the dust-collecting passage are peeled off from the surface of thedust-collecting electrode 22 by the gravity at the time of deposition orafter they have deposited in a prescribed thickness, for instance, about5 to about 20 mm, and they are let to fall. In order to collect thesefalling dust particles, it is possible to provide, as is illustrated inFIG. 4, a suitable dust collector 31 in the vicinity of the lower end ofthe dust-collecting electrode plate 22. For instance, a conveyormechanism may be adopted for this purpose. When it is desired toaccelerate the peeling and falling of the dust particles adhered to theelectrode surface, it is possible to impart a vibration to the surfaceof the dust-collecting electrode by means of a hammer member which isactuated intermittently. It is also possible to employ as thedust-collecting electrode plate 22 a dust-collecting electrode whichmoves intermittently or continuously (such as a belt or continuous film)and to effect the dust collection and the peeling of the dust particlesin different zones.

Various modifications may be made to the apparatus of this invention asfar as they do not deviate from the essence of this invention. Forinstance, as illustrated in FIG. 6, an electrode 22 of a plate form or anet-like or cloth-like form may be used as the dust-collectingelectrode. Such electrode is disposed in parallel to the chargingelectrode 21 of a fine wire form with a certain distance formedtherebetween. An overflowing tank or feed pipe 32 is provided at theupper end of said electrode 22' to form a continuous water film on theelectrode 22' and lets it flow downwardly, and a recovery tank 33 isprovided in the vicinity of the lower end of the electrode 22 to recoverwater which has flown downwardly on the electrode 22'. Morespecifically,

during the dust-collecting operation or the operation of cleaning theelectrode surface, water is fed from a store tank 34 through a pump 35and a pipe 36 to the overflowing tank or feed pipe 32 provided at theupper end always the charging electrode of a fine wire form, in

order to prevent deposition of dust particles or mists thereon. For thispurpose, in the embodiment illustrated in FIGS. 7 and 8, dust-collectingelectrodes 22, 22' and 22" are disposed on both side walls 14 and 14' ofthe ventilating chamber in the longitudinal direction of the'ventilatingchamber. Pairs of insulators 23-a and 23-a, 23-b, and 23-h, are fittedon the upper and lower ends of dust-collecting electrodes 22'(22"),respectively. Charging electrodes 21 (21) are stretched so as to connectconfronting insulators 23-a and 23-a, 23-1) and 23-h, at end pointsthereof and also to con nect two adjoining insulators 23-0 and 23-12,23-i b and 23-4.", Rotary shafts 41 (41) driven by a motor M andsupported by insulators 39 and 40 (39' and 40') are mounted on the outerportions of both side walls 14' and 14" of the ventilating chamber, andreels 42 and 43 (42' and 43') are fitted on the rotary shafts 41 (41 towind or unwind charging electrodes 21 and 21' of a fine wire form. Thus,the charging electrodes 21 (21) of a fine wire form extend from reels 42(43) to reels 42' (43) through the top ends of insulators 23-0, 23-a,23-h, 23-h, At the dust-collecting operation, when one of the rotaryshafts, for instance, the shaft 41, is driven by the motor M (at thistime the other rotary shaft 41' is kept free), charging electrodes 21(21') of a fine wire form are unwound from reels 42 (43'), travelthrough end points of each insulator and are wound onto reels 42 (43)fitted on the rotary shaft 41. When charging electrodes are allowed totravel in the above-mentioned manner during the dust-collectingoperation, deposition of dust particles or mists on charging electrodescan be prevented, and if they deposit on the charging electrodes, theymay be effectively removed by the contact of the charging electrodeswith end points of insulators or reels. The travelling rate of thecharging electrode of a fine wire form varies considerably depending onthe kind and amount of dust particles or mists to be removed, but ingeneral, it is preferred that the charging electrode is allowed totravel at a rate in an order of 50 to 500 mm per minute. When one of thereels is full of the electrode wire, the other reel is rotated and thewinding is effected in the reverse direction.

In this invention, the procedure of introducing a dust particleormist-containing gas into the dust-collecting zone is not particularlycritical, as far as it is introduced into the dust-collecting zone inthe form of an upward current. However, in case this invention isapplied to removal of an iron oxide fume formed in a casting house, itis preferred to adopt a method comprising projecting a gas upwardly froma gas projection opening which is provided on the floor of the castinghouse to surround the exposed portion of a tap hole portion or ironrunning in the casting house, and allowing an iron oxide fume formedfrom molten pig iron passing through the tap hole portion or ironrunning to move upwardly in a space wrapped with an upward current ofthe gas projected from said projection opening.

An iron oxide fume rising from molten pig iron being delivered from theblast furnace has a relatively high initial speed, for instance, about10 m/sec, and therefore, it has a great tendency to scatter around. Inthe above-mentioned embodiment of this invention, by forming an upwardcurrent of a gas rising so as to wrap the exposed portion of the taphole portion or iron running, it is made possible to introduce the ironoxide fume into the dust-collecting zone arranged in the ventilatingchamber provided in the upper portion of the building of the castinghouse without scattering of the fume or filling of the fume in theworking area of the casting house.

In the above embodiment of this invention, the gas projection opening tobe provided on the floor of the casting house may be disposed in thevicinity of both side edges of the tap hole portion or iron running atthe exposed port thereof. For instance, when the entire of the tap holeportion or iron running is exposed, projec tion openings may be disposedthroughout along both side edges of the tap hole portion or ironrunning. In case a part of the tap hole portion or iron running isexposed and the remaining part is wrapped with a covering, projectionopenings may be disposed along both side edges of the tap hole portionor running only at the exposed portion thereof. In case a part of thetap hole portion or iron running is wrapped with a covering, a smokeexhaust duct may optionally be mounted on said covering.

The gas projection opening and dust-collecting device may be mounted byvaious methods. For instance, in FIGS. 9 and 10, a tap hole portion 4'formed on the floor of a casting house 5 and an iron running 7 connectedto the tap hole portion 4' are partially covered with coverings 47-a,47-b and 47-c, and exposed portions 48-a, 48-b and 47-c are left forinspection of flow of molten pig iron. As is illustrated in FIG. 10, gasprojection openings 60 and 60' are provided on the floor 5 of thecasting house at the exposed portions 48-a, 48-b and 48-c of the taphole portion 4' or running 7 along both side edges of the running 4' or7, namely in the vicinity of both side edges of a refractory 49constituting the running, to project a gas in the form of an upwardcurrent. Lower ends of gas projection openings 60 and 60' are opened tothe insides of feed ducts 61 and 61'. A suitable gas such as air is fedto feed ducts 61 and 61' from a suitable source 62 of compressed airthrough a pipe 63, and projected through gas projection openings 60 and60' to rise in the working area 65 of the building 10 in the form ofupward currents 64 and 64'. Thus, a space 66 wrapped with upwardcurrents 64 and 64' of the gas is formed at the exposed portions 48-a,48-b and 48-c of the tap hole portion 4 and iron running 7. A fume 68 isformed from molten pig iron 67 flowing on the tap hole portion 4 andrunning 7, and this fume 68 moves upwardly in the form of an upwardcurrent in the interior of the space 66 wrapped with upward currents 64and 64 of the gas. Accordingly, in this embodiment of this invention, aspace wrapped with an upward current of a gas projected from the gasprojection opening is formed above the exposed portions of the tap holeportion 4' and iron running 7, and an iron oxide fume formed from moltenpig iron rises in this space in the form of an upward current.Therefore, the working area in the building of the casting house is notentirely filled with the iron oxide fume, and the working environment inthe casting house can be highly improved. Furthermore, gas projectionopenings 60 and 60 necessary for controlling the flow direction of theiron oxide fume and preventing the iron oxide fume from scatteringaround are provided on the floor of the casting house, and it isunnecessary to provide a device projecting in the space of the castinghouse, such as an exhaust duct, with the consequence that during theiron delivery operation or at the stoppage of this operation,performance of various other operations in the casting house is nothindered at all. Further, at the iron delivery operation, inspection ofthe flow of molten pig iron and sampling and examination of molten pigiron can be readily conducted without any particular trouble. Still inaddition, since gas projection openings are provided in the vicinity ofboth side edges of the exposed portions of the tap hole portion or ironrunning, if a worker comes close to the tap hole portion or iron runningby mistake, he can readily know from the presence of the projection flowof the gas that he has come close to the tap hole portion or ironrunning, with the result that a danger of his falling on molten pig ironcan be greatly reduced. Moreover, since the circumference of the taphole portion or iron running is shut off by the upward current of thegas projected from the gas projection opening, a great heat-insulatingeffect can be attained.

Since the iron oxide fume rising from molten pig iron has a relativelyhigh initial speed, it moves upwardly at a relatively high speed in aspace wrapped with the projection flow of the gas. Of course, if thespeed of the iron oxide fume is heightened by the upward current of theprojected gas, no trouble or disadvantage is brought about. The flowrate of the gas projected from the gas projection opening 60 or 60'varies greatly depending on the height of the building of the castinghouse, the slit width of the projection opening and other factors, butin general, it is preferred that the flow rate of the projected gas iswithin a range of from 50 to 150 m/sec, especially from 100 to 150m/sec. It is generally preferred that the slit width of the projectionopening is within a range of from to 40 cm, especially from to 40 cm.

The iron oxide fume rising in the form of an upward current in the spacewrapped with the gas projected from the gas projection opening reachesthe ventilating chamber provided in the upper portion of the building isintroduced in the dust-collecting apparatus detailed hereinabove.

As described above, the process of this invention is very effective forremoving dust particles of iron oxide formed during the molten pig irondelivery operation in the casting house ofa blast furnace. Those skilledin the art will apparently understand that such excellent effects canalso be attained in removal of dust particles of iron oxide formed inworking areas of buildings at various operations conducted in openhearth furnaces, convertors or electric furnaces in iron mills. Ofcourse, the process of this invention can be effectively applied toremoval of dust particles of iron oxide formed in buildings of ironfoundries treating molten pig iron. Still further, the dust-collectingprocess and apparatus of this invention may be utilized broadly forremoval of dust particles or mists formed in buildings of chemicalfactories during the working of calcination furnaces,

roasting furnaces, drying furnaces or melting furnaces or during otheroperations.

The term dust particles or mists" is used in the broadest sense in theinstant specification to include any particulate contaminant-containinghigh temperature gas, and it must be noted that the term is used toexpress the concept including fine solid or liquid particles suspendedin the air and mixtures thereof, and that so called fumes and fogs areincluded in this concept. Further, the high temperature gas includes allof gases that have a temperature higher than ambient temperature andform an upward current by natural ventilation.

By dint of the above-mentioned characteristics, this invention canattain a great technical advantage that dust particles or mists can beeffectively collected and removed from dust particleor mist-containinggases without reducing the efficiency of workings in buildings andwithout employing an exhaust duct or exhaust fan.

What 1 claim is:

l. A method for electrostatic dust collection which comprisesintroducing a particulate contaminantcontaining high temperature gasformed in the lower portion of a building into a dust-collecting passageprovided with a charging electrode of a fine wire form and adust-collecting electrode face confronting to said charging electrode,said dust-collecting passage being formed in a ventilating chamberprovided in the upper portion of the building and connected with asuction port mounted at the lower end of said ventilating chamber and anexhaust port mounted on a roof or side wall of said ventilating chamber;forwarding said particulate contaminant-containing high temperature gasthrough said dust-collecting passage in which an electrostatic field isformed between said charging electrode of a fine wire form and saiddust-collecting electrode face, along said charging electrode of a finewire form and substantially in parallel thereto; thus catchingparticulate contaminants contained in the high temperature gas on thedust-collecting electrode face; and discharging the gas from whichparticulate contaminants have been substantially removed, into theexterior of the ventilating chamber.

2. A method set forth in claim 1 wherein the average field intensity insaid dust-collecting passage is within a range of from 1.0 to 2.5 KV/cmand the particulate contaminant-containing high temperature gas isallowed to pass through said dust-collecting passage so that theresidence time of the gas in the dust-collecting passage is at least 5seconds.

3. A method set forth in claim 1 wherein the particulatecontaminant-containing high temperature gas is allowed to pass throughsaid dust-collecting passage so 7 that the linear velocity of the gas inthe dust-collecting passage is within a range of from 0.3 to 3 m/sec.

4. A method set forth in claim 1 wherein the particulatecontaminant-containing gas is introduced into said dust-collectingpassage in the form of an upward current owing to natural convention.

5. A method for dust collection in a casting house which comprisesprojecting a gas upwardly from a gas projection opening which isprovided on the floor of the casting house to surround the exposedportion of a tap hole portion and iron running; allowing an iron oxidefume formed from molten pig iron passing through the tap hole portionand iron running to move upwardly in a space wrapped with an upwardcurrent of the gas projected from the gas projection opening;introducing the rising iron oxide fume into a dustcollecting passageprovided with a charging electrode of a fine wire form and adust-collecting electrode face confronting to said charging electrode,said dustcollecting passage being formed in a ventilating chamberprovided in the upper portion of a building of the casting house;forwarding said iron oxide fume through said dust-collecting passage inwhich an electrostatic field is formed between said charging electrodeof a fine wire form and said dust-collecting electrode face, along saidcharging electrode of a fine wire form and substantially in parallelthereto; thus catching dust particles of iron oxide on thedust-collecting electrode face; and discharging the gas from which dustparticles of iron oxide have been substantially removed, into theexterior of the building.

6. Apparatus for electrostatic dust collection which comprises a workingarea provided in the lower portion of a building in which a particulatecontaminantcontaining high temperature gas is formed; a ventilatingchamber provided in the upper portion of the building, said ventilatingchamber being connected with said working area through a suction portmounted at the lower end of the ventilating chamber and opened to theopen air through an exhaust port mounted on a roof or side wall of theventilating chamber; and a dustcollecting passage formed in saidventilating chamber and composed of a charging electrode of a fine wireform supported by an insulating member and a dustcollecting electrodeface confronting to said charging electrode, an electrostatic fieldbeing formed between said charging electrode and said dust-collectingelectrode face; said dust-collecting passage having such a length thatthe residence time of the particulate contaminant-containing gas passingthrough the inside of the dust-collecting passage by natural conventionis at least seconds and said charging electrode of a fine wire formbeing laid along the direction of the advance of the particulatecontaminant-containing gas in the dust-collecting passage.

7. The apparatus of claim 6 wherein said charging electrode is composedof an electrically conductive fine wire having a diameter not exceeding1 mm.

8. The apparatus of claim 6 wherein a gas exhaust port is mounted on theside wall of the ventilating chamber on which the insulating member isfixed, and a cylindrical guide is mounted to surround said gas exhaustport and said insulating member whereby particulate contaminantsdepositing on said insulating member is wiped away by a gas currentflowing out of said gas exhaust port.

9. The apparatus of claim 6 wherein the length of said dust-collectingpassage is sufficient to provide a residence time of particulatecontaminant-containing gas passing through the inside of saiddust-collecting passage by natural convention to at least 10 seconds.

10. The apparatus of claim 6 wherein the dustcollecting electrodecomprises a plate member having a surface for forming a water film layerthereon, a water feed mechanism for feeding a water current downwardlyon said plate member, and a recovery tank for receiving the watercurrent having flown downwardly on the plate member.

11. The apparatus of claim 6 wherein said insulating member has an endportion supporting movably the charging electrode of a fine wire form,and said charging electrode of a fine wire form is travelled during thedust-collecting operation from a reel for unwinding said chargingelectrode of a fine wire form toward a reel for winding said chargingelectrode through said end portion of the insulating member.

12. The apparatus of claim 11 wherein the charging electrode of a finewire form is travelled at a rate of 50 to 5000 mm/min.

13. Apparatus for dust collection in casting houses, which comprises acasting house provided with a tap hole portion and an iron runningconnected with said tap hole portion; a gas projection opening providedin the vicinity of side walls of the exposed portion of the tap holeportion and iron running; and a dust-collecting passage formed in aventilating chamber provided in the upper portion of a building of thecasting house and composed of a charging electrode of a fine wire formand a dust-collecting electrode face confronting to said chargingelectrode, and electrostatic field being formed between said chargingelectrode and said dustcollecting electrode face; said gas projectionopening and dust-collecting passage being disposed in such a positionalrelationship that an iron oxide fume formed from molten pig iron passingthrough said tap hole portion and iron running rises in a space formedby an upward current of a gas projected from said gas projection openingand the iron oxide fume rising in said space is introduced into saiddust-collecting passage.

1. A method for electrostatic dust collection which comprisesintroducing a particulate contaminant-containing high temperature gasformed in the lower portion of a building into a dustcollecting passageprovided with a charging electrode of a fine wire form and adust-collecting electrode face confronting to said charging electrode,said dust-collecting passage being formed in a ventilating chamberprovided in the upper portion of the building and connected with asuction port mounted at the lower end of said ventilating chamber and anexhaust port mounted on a roof or side wall of said ventilating chamber;forwarding said particulate contaminant-containing high temperature gasthrough said dust-collecting passage in which an electrostatic field isformed between said charging electrode of a fine wire form and saiddust-collecting electrode face, along said charging electrode of a finewire form and substantially in parallel thereto; thus catchingparticulate contaminants contained in the high temperature gas on thedust-collecting electrode face; and discharging the gas from whichparticulate contaminants have been substantially removed, into theexterior of the ventilating chamber.
 2. A method set forth in claim 1wherein the average field intensity in said dust-collecting passage iswithin a range of from 1.0 to 2.5 KV/cm and the particulatecontaminant-contaIning high temperature gas is allowed to pass throughsaid dust-collecting passage so that the residence time of the gas inthe dust-collecting passage is at least 5 seconds.
 3. A method set forthin claim 1 wherein the particulate contaminant-containing hightemperature gas is allowed to pass through said dust-collecting passageso that the linear velocity of the gas in the dust-collecting passage iswithin a range of from 0.3 to 3 m/sec.
 4. A method set forth in claim 1wherein the particulate contaminant-containing gas is introduced intosaid dust-collecting passage in the form of an upward current owing tonatural convention.
 5. A method for dust collection in a casting housewhich comprises projecting a gas upwardly from a gas projection openingwhich is provided on the floor of the casting house to surround theexposed portion of a tap hole portion and iron running; allowing an ironoxide fume formed from molten pig iron passing through the tap holeportion and iron running to move upwardly in a space wrapped with anupward current of the gas projected from the gas projection opening;introducing the rising iron oxide fume into a dust-collecting passageprovided with a charging electrode of a fine wire form and adust-collecting electrode face confronting to said charging electrode,said dust-collecting passage being formed in a ventilating chamberprovided in the upper portion of a building of the casting house;forwarding said iron oxide fume through said dust-collecting passage inwhich an electrostatic field is formed between said charging electrodeof a fine wire form and said dust-collecting electrode face, along saidcharging electrode of a fine wire form and substantially in parallelthereto; thus catching dust particles of iron oxide on thedust-collecting electrode face; and discharging the gas from which dustparticles of iron oxide have been substantially removed, into theexterior of the building.
 6. Apparatus for electrostatic dust collectionwhich comprises a working area provided in the lower portion of abuilding in which a particulate contaminant-containing high temperaturegas is formed; a ventilating chamber provided in the upper portion ofthe building, said ventilating chamber being connected with said workingarea through a suction port mounted at the lower end of the ventilatingchamber and opened to the open air through an exhaust port mounted on aroof or side wall of the ventilating chamber; and a dust-collectingpassage formed in said ventilating chamber and composed of a chargingelectrode of a fine wire form supported by an insulating member and adust-collecting electrode face confronting to said charging electrode,an electrostatic field being formed between said charging electrode andsaid dust-collecting electrode face; said dust-collecting passage havingsuch a length that the residence time of the particulatecontaminant-containing gas passing through the inside of thedust-collecting passage by natural convention is at least 5 seconds andsaid charging electrode of a fine wire form being laid along thedirection of the advance of the particulate contaminant-containing gasin the dust-collecting passage.
 7. The apparatus of claim 6 wherein saidcharging electrode is composed of an electrically conductive fine wirehaving a diameter not exceeding 1 mm.
 8. The apparatus of claim 6wherein a gas exhaust port is mounted on the side wall of theventilating chamber on which the insulating member is fixed, and acylindrical guide is mounted to surround said gas exhaust port and saidinsulating member, whereby particulate contaminants depositing on saidinsulating member is wiped away by a gas current flowing out of said gasexhaust port.
 9. The apparatus of claim 6 wherein the length of saiddust-collecting passage is sufficient to provide a residence time ofparticulate contaminant-containing gas passing through the inside ofsaid dust-collecting passage by natural convention to at least 10secoNds.
 10. The apparatus of claim 6 wherein the dust-collectingelectrode comprises a plate member having a surface for forming a waterfilm layer thereon, a water feed mechanism for feeding a water currentdownwardly on said plate member, and a recovery tank for receiving thewater current having flown downwardly on the plate member.
 11. Theapparatus of claim 6 wherein said insulating member has an end portionsupporting movably the charging electrode of a fine wire form, and saidcharging electrode of a fine wire form is travelled during thedust-collecting operation from a reel for unwinding said chargingelectrode of a fine wire form toward a reel for winding said chargingelectrode through said end portion of the insulating member.
 12. Theapparatus of claim 11 wherein the charging electrode of a fine wire formis travelled at a rate of 50 to 5000 mm/min.
 13. Apparatus for dustcollection in casting houses, which comprises a casting house providedwith a tap hole portion and an iron running connected with said tap holeportion; a gas projection opening provided in the vicinity of side wallsof the exposed portion of the tap hole portion and iron running; and adust-collecting passage formed in a ventilating chamber provided in theupper portion of a building of the casting house and composed of acharging electrode of a fine wire form and a dust-collecting electrodeface confronting to said charging electrode, and electrostatic fieldbeing formed between said charging electrode and said dust-collectingelectrode face; said gas projection opening and dust-collecting passagebeing disposed in such a positional relationship that an iron oxide fumeformed from molten pig iron passing through said tap hole portion andiron running rises in a space formed by an upward current of a gasprojected from said gas projection opening and the iron oxide fumerising in said space is introduced into said dust-collecting passage.